Method and apparatus for measuring a change in surface level of a liquid

Abstract

A sensitive J-tube employs an indicating liquid in the U-tube portion for use with an immiscible liquid thereabove. The longer leg of the J-tube has a larger cross-section area portion containing the immiscible liquid when the J-tube has been immersed therein. The arrangement is such that the J-tube will amplify any changes in surface level of the liquid into which it is immersed, by producing a differential between levels of the indicating liquid in the U-tube legs. The principles are applied to a U-tube instrument to act as a manometer for measuring gas pressure differentials.

I claim: 
     
       1. Senstive J-tube instrument for measuring change in the surface level of a fluid in an underground tank or the like, comprising a U-tube portion containing an indicator fluid therein,   said U-tube portion having a predetermined inside cross-sectional area,   one leg of said U-tube portion being connected to a larger inside cross-sectional area tube to form the taller leg of said J-tube,   said larger inside cross-sectional area tube being long enough to extend from above the maximum surface level of said fluid being measured to below the minimum surface level thereof, and   valve means for connecting each of said U-tube portion legs with said fluid being measured and for isolating said taller leg,   said valve means being connected above the tops of said indicator fluid.   
     
     
       2. Measuring instrument according to claim 1, wherein said indicator fluid is immiscible with said fluid the change in surface level of which is to be measured.   
     
     
       3. Measuring instrument according to claim 2, wherein said indicator fluid has a density approximately the same but heavier than said fluid to be measured.   
     
     
       4. Measuring instrument according to claim 3, wherein said indicator fluid includes a coloring agent for visually distinguishing from said fluid to be measured.   
     
     
       5. Measuring instrument according to claim 4, wherein said valve means comprises a three-way valve.   
     
     
       6. Measuring instrument according to claim 5, further comprising a reservoir connected to the other leg of said U-tube portion at a location above the maximum expected height of said indicator fluid in order to contain any overflow without loss of indicator fluid.   
     
     
       7. Measuring instrument according to claim 6, further comprising an elongated support for suspending said instrument in said fluid to be measured.   
     
     
       8. Measuring instrument according to claim 7, further comprising elongated means for actuating said three-way valve from a location above the surface of said fluid to be measured.   
     
     
       9. Sensitive J-tube device for measuring change in the surface level of a fluid, comprising a relatively small inside diameter U-tube containing a predetermined quanity of a colored indicator-fluid that is immiscible with said fluid the surface level of which is to be measured,   said indicator-fluid having a density approximately the same but heavier than said fluid being measured,   a relatively large inside diameter tube connected to one leg of said U-tube and forming the taller leg of said J-tube,   said large tube being long enough to extend from above the maximum surface level of said fluid being measured to below the minimum surface level thereof,   a three-way valve having three ports for connection to each of the legs of said U-tube and to the body of said fluid being measured,   means for connecting said U-tube leg ports to said U-tube at a location that is above the maximum height of said indicator-fluid therein,   said three-way valve having at least three positions one for connecting all three of said ports together and one for connecting only the shorter leg of said J-tube to the body of said fluid being measured and one for closing said U-tube leg ports,   a reservoir connected into the shorter leg of said J-tube at a location above the maximum expected height of said indicator-fluid in order to contain any overflow without loss of indicator-fluid,   an elongated support for holding said J-tube device in a fixed position when a measurement is being taken, and   an elongated handle for actuating said three-way valve from a location above the surface of said fluid being measured.   
     
     
       10. Method of measuring a change in surface level of a fluid, comprising the steps of taking a relatively small inside cross-sectional area U-tube having an indicator-fluid therein,   connecting a larger inside cross-sectional area tube to one leg of said U-tube,   immersing said tubes into said fluid with said larger area tube extending above said surface level, connecting both legs of said U-tube with said fluid at a location on said tubes which is above the maximum height of said indicator-fluid therein,   said connection being made while said tubes are immersed,   disconnecting said one leg from said fluid to isolate said leg and said larger area tube from said fluid at the beginning of a measuring time period, and   determining the difference in height of the tops of said indicator-fluid levels in said U-tube at the end of said measuring time period whereby the change in surface level of said fluid is magnified.   
     
     
       11. Method of magnifying the measurement of a change in surface level of a first fluid by employing a U-tube containing a second fluid which is immiscible with said first fluid, comprising the steps of connecting a relatively large cross-section area tube to one leg of said U-tube at a location that is higher than a predetermined maximum level of rise of said second fluid in one of the legs of said U-tube,   connecting both legs of said U-tube into communication with said first fluid at a location above said maximum level prior to the commencement of a measurement time period,   immersing said U-tube and said large area tube in said first fluid to equalize the level of said first fluid inside of said large area tube with that outside and equalize the levels of said second fluid in said U-tube legs,   isolating said one leg and the large cross-section area tube from said first fluid at said commencement of said measurement time period, and   determining the difference in fluid levels of said second fluid in said U-tube legs at the termination of said measurement time period.